Power supply

ABSTRACT

A power supply ( 1 ) for a pulsed load ( 2 ) includes a first energy storage device in the form of a battery ( 3 ) which is in parallel with a second energy storage device in the form of a supercapacitor ( 4 ). Battery ( 3 ) and supercapacitor ( 4 ) are respectively modelled as: an ideal battery ( 7 ) in series with an internal resistance ( 8 ); and an ideal capacitor ( 9 ) in series with an equivalent series resistance (ESR) ( 10 ). Through use of a supercapacitor ( 4 ) having a low ESR with respect to the resistance ( 8 ), the power supply ( 1 ) facilitates continuity of supply to load ( 2 ). That is, during peak demand more of the load current will be supplied by supercapacitor ( 4 ) due to the lower ESR. Moreover, during times of lower load current demands the battery recharges the supercapacitor. This reduces the peak current needed to be provided by the battery and thereby improves battery longevity.

FIELD OF THE INVENTION

[0001] The present invention relates to a power supply.

[0002] The invention has been developed primarily for use with mobiletelephones and will be described hereinafter with reference to thatapplication. It will be appreciated, however, that the invention is notlimited to that particular field of use and is also suitable for otherelectronic devices, particularly portable devices such as Notebookcomputers, palmtop computers, electronic organisers, two-way pagers,remotely powered electronic device and the like.

BACKGROUND OF THE INVENTION

[0003] Pulsed loads occur in many battery-powered portable devices andthe peak current may be many times the resting current. When the batteryis nearly flat or is old, its' effective internal resistance tends toincrease, and it is less able to supply peak current demand without thedevice cutting out. Heavy load pulses generally also cause a largevoltage drop when they occur, and this may be detrimental to thebattery. Lithium-ion batteries are particularly susceptible to damage inthis way.

[0004] As a result, pulse loads invariably reduce battery run-time asthe load will have a minimum threshold supply voltage required at alltimes. When the load pulses and that voltage drop below the minimumthreshold, the electronic device must shut down as the voltageregulating circuitry is no longer able to supply the necessary voltageto run key circuits. However, at this time there may be useful energyremaining in the battery.

[0005] Moreover, some portable devices include protection circuitry thatshuts the device down if the current drawn from the battery exceeds apredetermined threshold. While this circuitry is designed to protect thebattery, it also results in shut down of the device when the peakcurrent, although being over the threshold, was so for only a shortperiod. This then requires the device to be restarted and, in some,cases, reconfigured. For mobile telephone and personal computingapplications this is a source of frustration to users.

[0006] Any discussion of the prior art throughout the specificationshould in no way be considered as an admission that such prior art iswidely known or forms part of common general knowledge in the field.

DISCLOSURE OF THE INVENTION

[0007] It is an object of the invention, at least in the preferredembodiment, to overcome or substantially ameliorate at least one of thedisadvantages of the prior art, or at least to provide a usefulalternative.

[0008] According to a first aspect of the invention there is provided anenergy storage device including:

[0009] a battery having a predetermined internal resistance R and twoterminals for allowing electrical connection to the battery; and

[0010] a supercapacitor connected in parallel with the terminals andhaving a predetermined equivalent series resistance ESR, whereESR<0.5.R.

[0011] Preferably, ESR<0.35.R. More preferably, ESR<0.25.R. As ESRdiminishes as a proportion of R, the pulsed load current provided by thesupercapacitor will increase. Accordingly, it is also preferred that thecapacitance provided by the supercapacitor is sufficient for the pulsedload profile to limit the battery current. More preferably, thesupercapacitor current during discharge is substantially constant.

[0012] According to a second aspect of the invention there is provided apower supply for a portable electronic device including an energystorage device described above.

[0013] According to a third aspect of the invention there is provided anenergy storage device including:

[0014] a battery for providing a battery current and having twoterminals for electrically connecting with a load; and

[0015] a supercapacitor connected in parallel with the terminals andhaving a predetermined capacitance that, in use, limits the batterycurrent to a predetermined threshold.

[0016] According to a fourth aspect of the invention there is provided apower supply including:

[0017] a battery for providing a battery current and having twoterminals for electrically connecting with a load that demands a pulsedcurrent; and

[0018] a supercapacitor connected in parallel with the terminals formaintaining the ratio of the RMS value of the battery current and theaverage value of the battery current at less than about 1.5.

[0019] Preferably, the supercapacitor maintains the ratio of the RMSvalue of the battery current and the average value of the batterycurrent at less than about 1.3. More preferably, the supercapacitormaintains the ratio of the RMS value of the battery current and theaverage value of the battery current at less than 1.1.

[0020] According to a fifth aspect of the invention there is provided anenergy storage device including:

[0021] a battery for providing a battery current and having twoterminals for electrically connecting with a load that demands a pulsedcurrent; and

[0022] a supercapacitor connected in parallel with the terminals formaintaining the ratio of the RMS value of the battery current and theaverage value of the battery current at less than about 1.5.

[0023] Preferably, the supercapacitor maintains the ratio of the RMSvalue of the battery current and the average value of the batterycurrent at less than about 1.3. More preferably, the supercapacitormaintains the ratio of the RMS value of the battery current and theaverage value of the battery current at less than 1.1.

[0024] According to a sixth aspect of the invention there is provided apower supply including:

[0025] a battery having two terminals for electrically connecting with aload that demands a pulsed current; and

[0026] a supercapacitor connected in parallel with the terminals formaintaining the ratio of the range of instantaneous power provided bythe battery and the average value of the power provided by the batteryat less than a predetermined threshold.

[0027] Preferably, the predetermined threshold is 1.5. More preferably,the predetermined threshold is 1. Even more preferably the predeterminedthreshold is 0.3.

[0028] According to a seventh aspect of the invention there is providedan energy storage device including:

[0029] a battery having two terminals for electrically connecting with aload that demands a pulsed current; and

[0030] a supercapacitor connected in parallel with the terminals formaintaining the ratio of the range of instantaneous power provided bythe battery and the average value of the power provided by the batteryat less than a predetermined threshold.

[0031] Preferably, the predetermined threshold is 1.5. More preferably,the predetermined threshold is 1. Even more preferably the predeterminedthreshold is 0.3.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Preferred embodiments of the invention will now be described, byway of example only, with reference to the accompanying drawing inwhich:

[0033]FIG. 1 is a schematic view of a power supply according to theinvention;

[0034]FIG. 2 is a schematic view of the power supply of FIG. 1illustrating the internal resistance of the battery and the equivalentseries resistance of the supercapacitor;

[0035]FIG. 3 is a chart demonstrating the discharge of a battery “with”and without a supercapacitor in parallel;

[0036]FIG. 4 is a sample of one of the discharge cycles of FIG. 3;

[0037]FIG. 5 is a schematic illustration of the transients that aregenerated in the power supply of a typical notebook computer;

[0038]FIG. 6 is a sample of the voltage and current waveforms in a powersystem of the Intel® Whidbey Notebook Platform without a supercapacitor;

[0039]FIG. 7 is a sample of the voltage and current waveforms in a powersystem of the Intel® Whidbey Notebook Platform with a supercapacitor inparallel with the battery;

[0040]FIG. 8 is a graph of the instantaneous power drawn from a batteryfor a notebook computer with and without a parallel supercapacitor;

[0041]FIG. 9 is a table that provides two additional examples ofsupercapacitors that are applicable for use in a power supply accordingto the invention;

[0042]FIG. 10 is a graph of the modelled performance of a power supplyaccording to the invention for use with a GSM mobile telephone load anda 50 second call cycle;

[0043]FIG. 11 is a graph of the modelled performance of a power supplyaccording to the invention for use with a GSM mobile telephone load anda 5 second on-time;

[0044]FIG. 12 is a graph of the modelled performance of a power supplyaccording to the invention for use with a GSM mobile telephone load anda 10 second on-time;

[0045]FIG. 13 is a graph of the modelled performance of a power supplyaccording to the invention for use with a GSM mobile telephone load anda 20 second on-time;

[0046]FIG. 14 is a graph of the modelled performance of a power supplyaccording to the invention for use with a GSM mobile telephone load anda 50 second on-time;

[0047]FIG. 15 is a table illustrating the use of the invention;

[0048]FIG. 16 is a drawing that is referred to in Annexure 1 as “FIG.1”;

[0049]FIG. 17 is a drawing that is referred to in Annexure 1 as “FIG.2”;

[0050]FIG. 18 is a drawing that is referred to in Annexure 1 as “FIG.3”;

[0051]FIG. 19 is a drawing that is referred to in Annexure 1 as “FIG.4”;

[0052]FIG. 20 is a drawing that is referred to in Annexure 1 as “FIG.5”;

[0053]FIG. 21 is a drawing that is referred to in Annexure 1 as “FIG.6”;

[0054]FIG. 22 is a drawing that is referred to in Annexure 1 as “FIG.7”; and

[0055]FIG. 23 is a drawing that is referred to in Annexure 1 as “FIG.8”.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] The following terms are used in the specification in thefollowing manner:

[0057] 1. “laptop computer” and “notebook computer” are usedinterchangeably and are intended to include portable computing devices,particularly those having on board rechargeable energy storage devices;

[0058] an ideal battery 7 in series with an internal resistance 8; and

[0059] an ideal capacitor 9 in series with an equivalent seriesresistance (ESR) 10.

[0060] Through use of a supercapacitor 4 having a low ESR with respectto the resistance 8, the power supply 1 facilitates continuity of supplyto load 2. That is, during peak demand more of the load current will besupplied by supercapacitor 4 due to the lower ESR. Moreover, duringtimes of lower load current demands the battery recharges thesupercapacitor. This reduces the peak current needed to be provided bythe battery and thereby improves battery longevity.

[0061] That is, this parallel hybrid combination of a supercapacitor anda battery allows a reduction in the voltage excursions under load,permitting the load to operate reliably until most of the battery'senergy has been used. This helps to protect the battery from potentiallydamaging voltage drops, of particular benefit to Lithium-ion batteries.

[0062] Conventional capacitors usually cannot support such loads formore than a few milliseconds. The supercapacitors used in the presentembodiments, however, have high capacitances so that, for a given loadcurrent, the peak current drawn from the battery will be limited.

[0063] Use of a hybrid battery-supercapacitor power supply, as envisagedby the invention, allows significantly better performance than can beachieved through use of a battery alone. Partly this is due to the muchlower effective internal resistance that is offered by thesupercapacitor, but also due to the large capacitances that areprovided.

[0064] The characteristics of the supercapacitor will, in part, bedriven by the battery and the load characteristics. However, it ispreferred that use is made of carbon double layer supercapacitors withoffer very high capacitance—from a few mF to hundreds of Farads—lowEquivalent Series Resistance (ESR)—1 mΩ and up—and low leakagecurrents—just a few μA. Such supercapacitors allow the design andimplementation of improved power supplies for portable devices that relyupon batteries as a primary source of energy storage.

[0065] The supercapacitors used in the preferred embodiments come in avariety of shapes, sizes and packaging to fit the space available. Oneparticularly preferred form is a thin prismatic form. Examples of suchsupercapacitors are provided in PCT patent application noPCT/AU99/01081, the disclosure of which is incorporated herein by way ofcross-reference.

[0066] The hybrid battery-supercapacitor allows the extended delivery ofthe current demand during transmissions or other severe loads, withoutthe terminal voltage dropping below an acceptable level.

[0067] The preferred embodiments provide a number of advantages, theseincluding:

[0068] Reduced voltage drop under load, giving extended run-time.

[0069] Reduced chance of battery damage from low voltage in Lithium-ionbatteries.

[0070] Reduced equivalent internal resistance compared with the batteryalone.

[0071] Flexibility in design, as use can be made of smaller batteriesthan normal, with higher internal resistance, at reduced cost.

[0072] Lithium ion batteries are widely used and, as stated above, areeasily damaged by high current pulses. These high current pulses causelarge voltage drops leading to premature shut down of the circuitrybeing supplied. These effects are both undesirable as they reducebattery life and battery run time. The preferred embodiments of theinvention, however, use supercapacitors to reduce the effectiveresistive voltage drop of the power supply combination and to reduce thecapacitive voltage drop. Accordingly, the run-time for portable batterypowered devices can be enhanced and premature shut down avoided.

[0073] By way of example, there is shown in FIG. 3 the discharge of abattery supercapacitor combination. The battery was a Li Ion battery asused on a Nokia mobile telephone and which has an approximate internalresistance of 100 mΩ. The discharge was alternately “With” and “Without”a supercapacitor in parallel during a 1A pulse discharge for 2 secondsduration, followed by 20 seconds off. The battery has been discharged toa state where it has little charge left, that is, when the potentialdifference is approximately 2.6 volts. The battery was then left tostand while the experiment was prepared and has recovered to asubstantially higher voltage. It is evident that the presence of thesupercapacitor in parallel with the battery provides a substantivedecrease in the resistive voltage drop.

[0074]FIG. 4 illustrates the characteristics of the voltage drops ingreater detail.

[0075] The supercapacitor used to provide the results in FIGS. 3 and 4had a capacitance of about 40 Farads and an ESR of about 5 mΩ.

[0076] The preferred embodiments of the invention are for use withbattery-powered devices that draw currents that vary greatly over time.For many devices, particularly mobile telephones, the variations occurover short time-scales during the normal operation of the telephone.

[0077] It will be appreciated that the losses in the power supplyconductors and the battery are proportional to the square of the currentthat flows through these components. The losses therefore increasesignificantly during high-current pulses, even if these pulses are shortin duration. However, the preferred embodiments, through theintroduction of a supercapacitor, reduce these losses by reducing theeffective resistance of the power supply as seen by the load. That is, asupercapacitor, as used in the present embodiments, has properties of:

[0078] 1. A low equivalent series resistance (ESR) relative to theinternal resistance of the battery;

[0079] 2. A high capacitance; and

[0080] 3. The ability to carry a high current.

[0081] “Low ESR” means a value that is much lower than the internalresistance of the battery. In one embodiment it has been found thatbenefit is derived where the ESR is half that of the internal resistanceof the battery. However, in more preferred embodiments, the ESR is aboutone quarter of the internal resistance of the battery preferably. Inother embodiments, the ESR is less than one tenth of the internalresistance of the battery.

[0082] Capacitance is regarded as being “high” relative to the peak loadcurrents involved. There is no single value of capacitance that isconsidered “high”, but it would typically be a capacitance that issufficient to be able to supply the peak load current for up to severalseconds without becoming discharged. This is, however, also dependentupon the load characteristics. If the load will not ever demand such asupply of current then the supercapacitor need not be configured toprovide it.

[0083] A “high current” supercapacitor is regarded in this context asone that is able to supply a load at least as great as that of thebattery, usually many hundreds of milliamps (mA) to several amps or tensof amps, without sustaining any damage.

[0084] As referred to above, resistance losses increase with the squareof the current. Given this, a current with a given average value willgenerate higher losses the greater the magnitude of variations in thecurrent, because of the increased losses during current peaks. Theinvention applies this principle through the use of a supercapacitorthat is able to smooth the variations in a current to reduce the lossesgenerated by that current. That is, the internal resistance of a batteryis thought to be a source of losses when current is drawn from thebattery and the variation in that current is reduced by thesupercapacitor. The current variations are predominantly borne by thesupercapacitor but, as it has a much lower resistance, the lossesgenerated are correspondingly smaller. Stating this another way, thesupercapacitor filters the current waveform as seen by the battery insuch a way that the supercapacitor carries most of the rapid changes inload current. During operation of the portable device, the battery willcarry a current that has a waveform with greatly reduced variations anda value that is much closer to the average load current than was thecase without the supercapacitor. Thus, the peak currents carried by thebattery will be reduced significantly, reducing the losses in the powersupply (the conductors and the supercapacitor) and protecting thebattery from high current pulses that are potentially harmful to it.

[0085] To optimise the benefit of the invention and the use of asupercapacitor to filter the current ripple, the preferred embodimentsutilise low resistance connections and conductors between the battery,the superconductor and the regulator circuitry from the portable device.As a guide, the connection resistances should be in total a smallfraction of the ESR of the supercapacitor. The conductors between thesupercapacitor and the load should have as low a resistance as caneconomically be achieved. As will be appreciated by the skilledaddressee, these parameters are varied to accommodate the inevitablecompromise between performance and cost.

[0086] When operating at low temperatures, such as −20° C., many typesof battery, such as those using certain common Lithium-ion chemistry,cannot supply the current peaks required by their loads without theirvoltages dropping excessively. This causes the portable devices to turnoff before the batteries are actually depleted. In more extreme cases ithas been found that even fully charged batteries are prone to theselarge voltage drops. However, with use of the preferred embodiments ofthe invention, a power supply is provided which includes asupercapacitor that is connected in parallel with the battery. Thelow-pass filter effect of the supercapacitor—as described above—resultsin the battery being exposed to a reduced peak current. The battery thusprovides a current that is relatively constant and approximately equalto the average current drawn by the load, and the battery is able tocontinue to operate the portable device until it is either fullydepleted or unable to supply the lower, average current at the lowtemperature.

[0087] Many batteries contain electronic protection and control circuitsthat control the charging of the batteries, and/or protect the batteriesfrom high currents. While in some cases this circuitry is containedwithin the electronics of the load, in other cases it is containedwithin or attached to the housing of the battery. The protection andcontrol circuits are commonly designed to disconnect that battery fromthe load or to limit the peak current drawn from the battery and/or todisconnect the battery from the load if the battery's supply voltagedrops below a predetermined value. Given this, some preferredembodiments of the invention include a power supply having a battery ofthe type mentioned above in parallel with a supercapacitor. Thiscombination reduces the risk of the battery shutting down whenunexpected large transient currents are drawn.

[0088] The filtering effect described above also allows an extension ofthe run-time of a device to be achieved. That is, the battery is able toreach a lower voltage than is otherwise possible before the system mustbe shut down.

[0089] In some embodiments the addition of a low-ESR supercapacitor inparallel with the battery obviates the requirement for input-decouplingcapacitors. This, in turn, reduces costs for that part of the supply.

[0090] The low impedance of the supercapacitor also allows use ofbatteries with higher impedance and greater capacity than normal. Thisincreases the energy available to run the system, resulting again inincreased run-times.

[0091] During operation of the power supply according to the preferredembodiments, the supercapacitor is effectively connected directly inparallel with the battery, as shown in FIG. 1. In some embodiments thereare one or more switches in the supply circuit to enable the electronicdevice to be switched ON and OFF. It will be appreciated that theseswitches preferably have a low ON-resistance relative to the ESR of thesupercapacitor. Preferably also, there is no switch between thesupercapacitor and the electronic device, as this will, in some cases,reduce the benefit obtained from the supercapacitor.

[0092] In other embodiments the power supply includes an additionalcircuit for charging/discharging the supercapacitor gradually followingthe connection of that supercapacitor to a battery that is providing adifferent voltage. That is, the circuit is to limit the charge/dischargecurrents that flow through the supercapacitor and the battery.

[0093] The conductors in which the greatest losses occur are those inwhich the highest peak currents flow, all other things being equal.These are the conductors between the load and the supercapacitor.Therefore, to reduce these losses to a minimum, it is beneficial toplace the supercapacitor as close as possible to the load. Theconductors between the battery and the supercapacitor carry a steadiercurrent than the load current, and therefore the losses in theseconductors are reduced. For common battery-powered devices, peak loadcurrents are usually high, at least for short periods. This isparticularly true for pulsed load devices such as those utilisingdigital circuitry. The use of a suitable high-power supercapacitor inparallel with the battery, in accordance with the invention, allows areduction in the losses in the power system and battery and helps toprotect the battery from potentially harmful current pulses. This isachieved without requiring the use of expensive electronic circuitry andas the same time providing additional energy storage capacity for thedevice.

[0094] At low temperatures, a supercapacitor in accordance with thepresent invention also enables a portable electronic device to functionnormally when the battery would not be able to supply the peak currenton its own. That is, the use of the supercapacitor reduces the voltagedrop that is experienced at the supply terminals of the device and,hence, reduces the effect of a short transient peak load current fromshutting down of the device.

[0095] A power supply according to the preferred embodiments alsoimproves the accuracy of detection of a low-battery condition, as thesupercapacitor smoothes the battery voltage. This helps avoid apremature shutdown, and extends the battery run-time.

[0096] In some embodiments of the invention, the supercapacitor is partof a power supply for a notebook computer that also supports thenotebook's energy requirements during a battery change without the needto shut down or save data to disk. This functionality is more fullyexplored in the co-pending PCT application filed with the AustralianPatent Office on 15 May, 2001 in the name of Energy Storage Systems PtyLtd and which is numbered PCT/AU/01 . . . . The disclosure in thatco-pending application is incorporated herein by way of cross reference.

[0097] The power supply circuitry of the notebook computer was subjectto some minor changes to the DC-DC converters to accommodate thesupercapacitor. The result being an immediate increase in efficiency inthe converters of 5%, which translated to an increased run time of over3 minutes per charge out of 83 minutes total run-time. The measurementswere conducted on an Intel® Widbey platform using a Lithium ion batterywith a 7.2 Ah capacity in parallel with the supercapacitor. It will beappreciated that the Widbey platform operates on a supply voltage equalto two Lithium ion cells in series. This is generally lower than mostnotebooks, and provides cost savings in the simplifiedbattery-protection and balancing circuit. Costs are also reduced in theDC-DC converters, as a result of the low impedance of thesupercapacitor. That is, the need for the decoupling capacitors in theDC-DC converter is reduced if not eliminated. For example, some powerboards use as many as six decoupling capacitors.

[0098] Batteries designs have advanced mainly in the direction ofincreasing power density to supply the demands of notebooks and otherportable devices. At face value this does not contribute to theavailable run-time for the device by the battery as there will be acompromise in the stored energy for a given volume. However, due to thepulse nature of the usual loads being supplied by the battery, theeffectiveness of that battery to contribute to the operation of the loadis strongly dependent on its internal resistance. That is, the abilityof the battery to supply high power—even for short periods—is limited.This, in turn, affects the efficiency and operation of the DC-DCconverters in, say, a notebook PC. The protection circuits used inLithium ion battery packs further increase their effective internalresistance. The preferred embodiments of the invention, however, utilisea high-power supercapacitor—that has very low ESR—in parallel with thebattery. This provides a hybrid supply that is able to make use of thecombined attributes of high energy density and low source impedance.

[0099] The design of a DC-DC converter, such as that used in a notebookcomputer, is influenced by the nature of the energy source and the load.The output load of the DC-DC converter is, in some cases, microprocessorcontrolled, with clock-gated technology to reduce average powerdissipation. Clock-gated architecture produces large transients at theoutput of the DC-DC converter and, consequently, produces large ripplecurrents in the power input rail of the converter. Although DC-DCconverters have local decoupling to filter out the transient pulses, thelimitations of conventional capacitors, cost and PCB real-estate,insufficient or improper local decoupling often allow most of thetransients to reach the battery and its protection circuits. As aresult, the battery-protection circuit prematurely shuts down thesystem, causing a loss in operational battery life.

[0100] With the use of the invention which, in this embodiment, includesplacing a low-impedance supercapacitor in parallel with the battery, thetransient is “filtered” prior to reaching the battery and its protectioncircuit. The voltage at the battery terminals and the protection circuitremains relatively constant, preventing the protection circuit fromgenerating a premature low-battery warning. This enables the powersupply to maximise the available capacity of the battery. For thisembodiment the overall improvement was found to be 5%, which results inan increased battery run-time of more than 3 minutes in an 83-minutenormal run-time. However, for another embodiment that utilised a largercapacity supercapacitor, the average increase was about 10% additionalrun-time.

[0101] As will be appreciated by the skilled addressee, from theteaching herein, that the actual improvement in the run-time provided bythe supercapacitor will be dependent upon a number of factors includingthe characteristics of the battery, the supercapacitor and the load.

[0102] The inclusion of the supercapacitor in parallel with the batteryallows for modified charging algorithms, particularly for batteries ofthe Li-ion type. That is, the battery is able to be charged to fullcapacity more quickly than could safely have been achieved in absence ofthe supercapacitor.

[0103] The above tests were also conducted using the Intel® Whidbeyplatform. The platform operates on a supply voltage of two sets of fourLithium ion cells each, with the cells in each set in parallel. In othernotebook computers use is more typically made of three or four sets ofparallel pairs of Lithium ion cells connected in series. The inventionis suitable for use with both these battery configurations, as well asothers.

[0104] Typical notebook batteries have an internal resistance of over100 mΩ, made up of:

[0105] 1. The cells' internal resistance of about 50 mΩ for a single1800 mAh cell, with typically three or more parallel pairs in series;

[0106] 2. A 10 mΩ current-sense resistor; and

[0107] 3. A 20 mΩ ON-resistance FET used as an output switch.

[0108] The internal resistance of a reduced-voltage battery, like thatused in the measurements referred to above, is about 63 mΩ. This is madeup of a series combination of two sets of three cells in parallel, plusthe sense resistor and FET mentioned above. In use, the battery iscomprised of two parallel pairs in series which, together with theprotection circuits, provide a total internal resistance ofapproximately 80 mΩ.

[0109] Connecting a supercapacitor—such as that manufactured by cap-XXPty Ltd and designated as Mk 2 S/C—in parallel with the battery reducesthe source impedance still further. In this embodiment, the nominalresistance of the supercapacitor is less than 5 mΩ and, hence, theparallel combination of battery and supercapacitor is lower still. Sincethe supercapacitor's ESR is only about 6% of the battery's internalresistance, it is the supercapacitor that takes the brunt of all currentsurges. Consequently, whenever the load current increases suddenly, suchas during a CPU transient, the supercapacitor is able to provide most ofthe initial current surge. This smoothes the battery voltage and reducesbattery ripple current, resulting in increased accuracy of detection ofa low-battery condition.

[0110] The surge-current capability of the supercapacitor also reducesthe I²R losses in all resistances between the supercapacitor itself andthe battery, including those in the battery, since the current peaks inthat part of the circuit are reduced.

[0111]FIGS. 6 and 7 are comparative samples of the voltage and currentwaveforms in a power system of Intel® Whidbey Notebook Platformrespectively without and with a supercapacitor according to theinvention. For FIG. 6:

[0112] 1. The top trace is the battery voltage.

[0113] 2. The square wave is the load current, shown in 2 A/div.

[0114] 3. The waveform superimposed on the square wave is the batterytransient current, shown in 500 mA/div; and

[0115] 4. The bottom trace is a signal proportional to instantaneouspower drawn from the battery, which is a product of battery voltage andcurrent.

[0116] For FIG. 7:

[0117] 1. The top trace is the battery voltage. Note that the inclusionof the supercapacitor has eliminated the large ripple seen in FIG. 6,leaving only a little high-frequency noise from the DC-DC converter;

[0118] 2. The square wave is the load current, which is shown in 2A/div;

[0119] 3. The waveform superimposed on the square wave is the batterytransient current, and is shown in 500 mA/div. Note that the presence ofthe supercapacitor has eliminated the major variations in batterycurrent seen in the corresponding trace in FIG. 6, leaving a nearlystraight line;

[0120] 4. The bottom trace is a signal proportional to the instantaneouspower drawn from the battery and is a product of battery voltage andcurrent. The supercapacitor has removed the large power variationsvisible in FIG. 6.

[0121]FIG. 8 is a graphical comparison of the instantaneous power drawnfrom the battery with and without a parallel supercapacitor The verticallines represent the range of instantaneous power drawn from the batteryand the horizontal marker on each represents the average power drawnduring the test.

[0122] The longest three vertical lines are the power drawn from thebattery alone in three separate tests. The power draw without asupercapacitor in parallel with the battery varied between 800 mW and9500 mW. The shortest three vertical lines are the range of power drawfrom the battery itself when a supercapacitor was in parallel with it.Three different supercapacitors were used, and the results were verysimilar, in spite of the range of ESR for the supercapacitors. This isattributable to the low ESR of all the supercapacitors, relative to theinternal resistance of the battery. From left to right, the supercapsidentified by the designations Mk2 S/C#1, Mk1 S/C#1 and Mk2 S/C#2 werecharacterised by approximate capacitances and ESRs of 40 Farads and 4mΩ, 50 Farads and 7.8 mΩ, and 50 Farads and 7.6 mΩ. Based upon theapproximate 80 mΩ internal resistance of the battery being used, thisresults in respective ratios of ESR to internal resistance of 5.0%, 9.8%and 9.5%.

[0123] In other embodiments use is made of higher-ESR supercapacitorsdue to lower cost. Notwithstanding, there is considerable gain to behad.

[0124] Supercapacitors for use in the preferred embodiments of theinvention are manufactured in accordance with the application. In someembodiments the supercapacitors are thin and light, with variableform-factors. In other embodiments, however, the supercapacitors arecontained within a rigid housing. Single supercapacitor cells are ratedfor continuous use at 2.3 Volts, with a maximum of 2.5 Volts, althoughshort transients at higher voltages are tolerable. For embodimentsoperating at higher voltages, the supercapacitor is made up of a seriescombinations of supercapacitor cells.

[0125] The current rating of the supercapacitor is also determined bythe nature of the application. While in some embodiments the charging,discharging or ripple currents are in the order of milliamps, in otherembodiments these currents are in the order of 20 Amps or more.

[0126]FIG. 9 is a table that provides two additional examples ofsupercapacitors that are applicable for use in a power supply accordingto the invention.

[0127] Previous investigations have shown that after a battery isdischarged it will eventually recover to be close to the initial voltagebefore the current was drawn if the discharge is not too long or toodeep. This effect occurs due to concentration depletion of electroactivespecies at the electrode surfaces within the battery during discharge.Once the discharge ends then the molecules equilibrate to regenerate auniform concentration that is lower than the initial concentration dueto the flow of electrons that occurred during the discharge. Thedischarge and the equilibration are primarily diffusive and aretherefore believed likely to depend upon the square root of time.

[0128] Modelling battery behavior using Pspice enables some aspects ofthis phenomenon to be explored. The present applicants commissioned sucha model to be investigated, and this was the subject of an unpublishedpaper by Dr J. G. Rathmell entitled “PSPICE MODELLING OFBATTERY/SUPERCAPACITOR DISCHARGE” dated 12 Jul., 1999. A copy of thispaper is incorporated as part of this specification and marked asAnnexure 1. The drawings referred to in Annexure 1 as “FIG. 1”, “FIG. 2”and so on are contained within this specification as part of the figuresand are labelled respectively as FIG. 16, FIG. 17 etcetera.

[0129] This modelling has been applied by the inventors to develop thepreferred embodiments of the present invention. Particularly, themodelling was expanded upon and adapted to the case of a pulsed loadsuch as that used in a GSM type mobile telephone. In the battery model aRC circuit with a characteristic time constant and a look-up table areused to describe the effect. The modelling conditions involved the useof the AAA alkaline battery with the RMS rate loss model which has aninternal resistance of 0.6 ohm, a capacity of 1.2 Ah and a timeconstant, τ, of 10 seconds. Two values of IRATIO (I_(RMS)/I_(average))were used, a value of 1.02 to simulate a battery and supercapacitorcombination—as is achieved in practice—and 1.62 for the battery alonewith the average current being equal to 0.3 Amps based on a GSMwaveform.

[0130]FIG. 10 and FIG. 15 contains the results of the above modellingwhich accords with practical implementations of the preferredembodiments of the invention. That is, it is clearly demonstrated thatthe presence of the supercapacitor in parallel with the battery isbeneficial because it reduces the depth of the discharge. Additionally,the effect of matching the discharge cycle to the battery recovery rateis shown. The useable capacity is calculated from the time that it takesthe discharge to reach down to 0.7 V and the total available time isobtained from the rated capacity and the average current. In conclusion,while is better to take a lot of “small bites” of energy rather than afew “big bites’ of energy, there is still considerable benefit to be hadfrom the use of the supercapacitor even if “big bites” are taken.

[0131] FIGS. 11 to 14 demonstrate the effect of on-time, expressed as afraction of the time constant, on the battery performance. Once againthe battery capacity is calculated from the rated capacity and theaverage current, the time constant of the battery is 10 seconds and theinternal resistance is 0.6 ohm. These graphs more clearly demonstratethe effect of minimizing the depth of discharge. It is also noticeablethat while the “supercapacitor advantage” is diminished under conditionswhere the “depletion” effect becomes apparent, there is stillconsiderable advantage to be gained.

[0132] Given the relationship between battery current, which is thesubject of the investigation of the modelling referred to above, and thepower provided by the battery, it becomes clear, from the teachingherein, that the power consumption characteristics shown in FIG. 8 areentirely consistent with the modelled current characteristics.

[0133] Although the invention has been described with reference tospecific examples it will be appreciated by those skilled in the artthat it may be embodied in many other forms.

PSpice modelling of battery/supercapacitor discharge report ofinvestigation by Dr JG Rathmell 12 Jul. 1999 for cap-XX Pty Ltd CONTENTS

[0134] summary

[0135] introduction/scope

[0136] supercapacitor models

[0137] battery models

[0138] discharge simulation

[0139] discUssion/further work

[0140] references

[0141]FIG. 1 ac analysis

[0142]FIG. 2 transient analysis

[0143]FIG. 3 battery model

[0144]FIG. 4 lost rate

[0145]FIG. 5 effect of RSER

[0146]FIG. 6 effect of CAP

[0147]FIG. 7 10s simulation

[0148]FIG. 8 full discharge

[0149] Appendix 1 PSpice file of FIG. 1

[0150] Appendix 2 PSpice file of FIG. 2

[0151] Appendix 3 PSpice file of FIG. 5

[0152] Appendix 4 PSpice file of FIG. 6

[0153] Appendix 5 PSpice file of FIG. 7

[0154] Appendix 6 PSpice file of FIG. 8

[0155] Appendix 7 model library

SUMMARY

[0156] A library of PSpice macromodels has been developed forsupercapacitors and batteries. Battenes covered are lead-acid, alkaline,Nicad, Nimh and Lithium-ion. These models have been modified toincorporate capacity lost under fast pulsing. Simulations have beendone, demonstrating supercapacitor impedance and phase, batterydischarge and extension of battery life/capacity with supercapacitor.

INTRODUCTION/SCOPE

[0157] The scope of this report is the development of a library ofPSpice battery models and the investigation of PSpice simulation ofbattery/supercapacitor discharge under East pulsing, in particular theextension of battery capacity by the use of a parallel supercapacitor.Battery models are for lead-acid, alkaline (N, AAA, AA, C, D & 9V),Nicad, Nimh and Lithium-ion. These models were largely gathered fromliterature [1-3], with modifications and corrections. Supercapacitormodels implemented are the RCCPE model provided by cap-XX [4]. Noverification of models with experiment was undertaken.

Supercapacitor Models

[0158] Supercapacitors are described in [4]. The model ofsupercapacitor, and parameters, used in simulation are as provided bycap-XX in [4] and in correspondence. The model is a simple R, C plusconstant phase term (RCCPE), describing frequency-dependent impedance;$\begin{matrix}{{Z(s)} = {R + \frac{1}{s\quad C} + \frac{1}{T\quad s^{P}}}} & (1)\end{matrix}$

[0159] where R is series equivalent resistance (SER), C capacitance, T amagnitude, P exponent and s=jw.

[0160] This model was implemented using the PSpice Laplace analogbehavioural modelling form. Three forms of this model have beenimplemented; SUPER1 directly specifying the equation, SUPER2incorporating a delay term and SUPER3 resolving the CPE term as separatereal and imaginary terms (see Appendix 7). These were forexperimentation and are equivalent (except for the delay). Alsoimplemented is model RCTEST, a simple series RC circuit for comparisonwith supercapacitor models.

[0161] Note that the CPE term is interpreted by PSpice as having anon-causal impulse response, with a warning message given. A delay term(e^(−sa)) is suggested by PSpice to resolve this. Such a delay alterssimulation results in ways that would require experimental verification.As the non-causal impulse response is not a problem for the ac andtransient analyses done here, this warning is ignored. Ultimately, theRCCPE model should be altered to be applicable over the full frequencyrange that PSpice considers, possibly by convolving the s-model with asuitable filter function.

[0162]FIG. 1 shows impedance magnitude & phase as a function offrequency for the three supercapacitor models and the RCTEST model.Models SUPER1 & 3 are identical. These results compare with plotssupplied by capXX. FIG. 2 shows a transient analysis for the abovemodel, with similar results as FIG. 1. PSpice source files used in thesesimulations are given in Appendices 1 & 2. Models are contained inAppendix 7.

[0163] Limitations of the models are that parameters axe obtained fromstatic impedance spectroscopy. As such, they do not incorporatenon-linearity with applied voltage nor rate-dependent anomalies. Inparticular, the model has not been experimentally verified under thefast pulsing loads dealt with here. Nonetheless, it is assumed that themodels are reasonable.

Battery Models

[0164] Appendix 7 gives models for the batteries dealt with; lead-acid,alkaline (N, AAA, A, C, D, & 9V), Nicad, Nimh and Lithium-ion. Thesemodels were obtained from [1-3]. Some debugging, correction andmodification was done. Six alkaline styles were done because of theslightly different behaviours of these.

[0165]FIG. 3, from [1], shows the general form of these models. Modelsfor Nicad & Lithium-ion have additional terms for temperature. The Nicad& Nimh models also have correction terms for low-rate discharges.

[0166] All models consist of an output circuit (+OUTPUT, −OUTPUT) thatinvolves a battery voltage source and a series resistance. The V_Senseterm senses battery current for use in battery voltage correction. Therest of a model is concerned with correction of the battery voltage withdischarge rate, temperature, age, etc. All use look-up tables to relatebattery voltage to these.

[0167] Of particular interest here is the E_Lost_Rate term which seeksto model the electrochemical reduction in avaliable battery capacityunder heavy discharge. This is modelled as a non-linear function of thedelayed (by RC delay) discharge rate using a look-up table. FIG. 4 showsthe lost rate vs discharge rate for the batteries modelled.

[0168] In investigating the improvement of battery capacity with the useof a supercapacitor, it is principally lost rate that is involved. AsFIG. 4 shows, this reduction in battery capacity with discharge ratevaries from 10%-80%, depending on battery type. Thus the effectivenessof coupling a supercapacitor with battery will be strongly dependent onbattery type and load. Note also that this lost capacity recovers intime if the load is removed, so we are primarily concerned here withcontinuous loads.

[0169] The delay and recovery time constants of the lost rate alsovaries considerably with battery type; from 3 s for Nicad, Nimh &Lithium-ion, 10 s for alkaline to 60 s for lead-acid.

[0170] The battery models of Appendix 7 were designed to model dischargeunder relatively constant loads (having variation times much greaterthan the lost rate time constants, i.e. frequencies much less than 1Hz). This work is concerned with pulsed current loads of frequencygreater than 100 Hz. With these, lost rate is a function of rms loadcurrent, although still with delayed onset [1]. At these frequencies,electrochemical recovery of lost capacity does not occur between pulses.

[0171] For relatively constant load current, average and rms arecomparable, hence the extant models only relate lost rate to averagecurrent. For this work, these models have been modified to relate lostrate to the rms load current, through modification of the delayed andaveraged discharge rate used in lost capacity table look-up.

[0172] The circuit elements giving average lost rate are of the form;E_Rate RATE 0 VALUE = { I(V_Sense) / CAPACITY } R_2 RATE 60 10 ; R2-C1-> 10 Second time constant C_1 60 0  1 * E_Lost_Rate 50 SOC TABLE {V(60) } = . . .

[0173] These have been modified as follows to give rms lost rate;E_SQRate SQ_RATE 0 VALUE = { PWR ( I(V_Sense) / CAPACITY, 2 ) } R_SQSQ_RATE 60 10 ; R2-C1 -> 10 Second time constant C_SQ 60 0 1 * THIS NODEGIVES PROPER DISCHARGE RATE E_RATE RATE 0 VALUE = { SQRT( V(SQ_RATE) ) }R_RATE RATE 0 1G * E_Lost_RATE 50 SOC TABLE { SQRT( V(60) ) } = . . .

[0174] Appendix 7 contains two models for each battery type, MODEL_R andMODEL_A, using rms and average discharge rates respectively to calculatelost capacity. The _R models are used hereafter.

[0175] Temperature effects in the models already involve rms loadcurrent.

Discharge Simulation

[0176] The pulsed load used in this work is a pulsed current source, asmight be expected to be drawn from a battery by a regulator or DC-DCconverter. The pulse timing was chosen to reflect what might be expectedof a GSM telephone handset; 0.577 ms timeslot for transmission in a4.615 ms frame [5], i.e. a short heavy discharge during transmissionfollowed by very light discharge. Load current amplitudes were chosen toillustrate the lost rate effects. These require experimentalverification.

[0177] The objective of this work is to demonstrate improvement inbattery capacity, with fast pulsing, by the use of a parallelsupercapacitor. The battery effects of interest here are lost capacity,temperature and voltage dropout. Only lost capacity is investigatedhere, however, dealing with all three involves reducing battery pulsecurrent amplitude (hence voltage drop) through the supercapacitorsupplying the bulk of the pulse current and being recharged betweenpulses. Thus battery rms current is reduced, reducing lost capacity andinternal power dissipation (temperature).

[0178]FIG. 5 shows an ALK_AA_R model with supercapacitor for a GSM loadperiod, for three different supercapacitor resistances R_(sup). Appendix3 shows the PSpice source file. The reduction of battery current pulseamplitude and of voltage drop is related to the relative size of R_(sup)compared to the battery resistance R_(bat). It is R_(bat)//R_(sup) thatdetermines the drop. Thus, for best results, R_(sup) is much less thanR_(bat).

[0179]FIG. 6 (and Appendix 4) shows the same simulation with threedifferent values of C_(sup). The supercapacitor time constantR_(sup)C_(sup) should be large enough to substantially maintainsupercapacitor discharge for the duration of the pulse, and to spreadthe recharging over the load period. Thus supercapacitor time constantshould be greater than or equal to the load period.

[0180]FIG. 7 (and Appendix 5) shows pulsed discharge for the last cycleof a 10 second simulation, for an ALK_AA_R battery model, with andwithout supercapacitor. The supercapacitor used is the cap-XX E/CreditCard.

[0181] Of note here is the greater reduction in battery voltage andstate of charge (capacity) for the case of no supercapacitor.

[0182] The ALK_AA_battery model was used here as having a large lossrate with discharge. The supercapacitor used was chosen as having an RCto complement this battery. The load current amplitudes were chosen(1A_(rms), 0.44 A_(average)) to give maximum lost rate of 60%.

[0183] From FIG. 7, the supercapacitor reduces the battery load to 0.45A_(rms). At this level, the lost rate is 36%. The limit of battery rmscurrent would be, in this case, the load current average of 0.44 A. Thiswould give a lost rate of 35.4%.

[0184] Simulation time is a big issue here. The above 10 s simulationtook approximately 1000 s on a Pentium 100 (HP Omni 800 ct). To simulatefull battery discharge (several hours) would take over a week! Theproblem is that simulation time is related to circuit node activity, aswell as circuit complexity. With fast pulsing, node status (voltage &current) is changing rapidly. The timestep of simulation must then bevery small, relative to circuit time constants. Simulation takesapproximately 0.5 s per load period and full discharge involves severalmillion load pulses.

[0185] All is not lost. Of interest is the average current and themagnitude of the lost rates. The latter can be determined from FIG. 7.Battery models have been modified to incorporate a parameterIRATIO=I_(rms)/I_(average), with a default of 1. This is used to set thelost rate that would apply for a particular rms discharge rate, whensimulated under a constant load current I_(average). Under constantcurrent, simulation is very fast.

[0186] The previous circuit elements giving lost rate have been modifiedas follows to give proper rms lost rate under constant current; E_SQRateSQ_RATE 0 VALUE = { PWR( I(V_Sense) * IRATIO / CAPACITY, 2 ) } R_SQSQ_RATE 60 10 ; R2-C1 -> 10 Second time constant C_SQ 60 0 1 * THIS NODEGIVES PROPER DISCHARGE RATE E_RATE RATE 0 VALUE = { SQRT( V(SQ_RATE) ) }R_RATE RATE 0 1G * E_Lost_Rate 50 SOC TABLE { SQRT( V(60) ) } = . . .

[0187]FIG. 8 (and Appendix 6) shows such a simulation, taking 4 secondsto execute. Note that both cases (with & without supercapacitor) havethe same discharge rate, but the battery without the supercapacitorsuffers from a greater lost rate. Hence its discharge life time isconsiderably shorter (60% compared to 36%). This then demonstrates theincreased battery life with supercapacitor.

DISCUSSION/FURTHER WORK

[0188] The battery models, with modifications for rms discharge lostrate, enable simmulation of fast pulsed discharge, for both short andlong durations.

[0189] Limitations of this work are the lack of experimentalverification of both battery and superconductor models under fastpulsing loads.

[0190] Further should involve;

[0191] verification of battery fast pulsing lost rate modelling,

[0192] improvement of battery models under fast pulsing, throughmeasurement and model fitting,

[0193] extension of supercapacitor models for both non-linearity andrate dependencies, through measurement and model fitting, andaccuracy/granularity of the piece-wise linear table functionsrepresenting lost rate,

[0194] elaboration of supercapacitor design and application criteria,for a range of batteries and loads (selection of supercapacitor R & C),and

[0195] measurement of real load currents.

References

[0196] 1. “Simple PSpice models let you simulate common battery types”,S C Hageman, EDN October 1993,pp.117-132

[0197] 2. “PSpice models nickel-metal-hydride cells”, S C Hageman, EDNFeb. 2, 1995, p99

[0198] 3. “A PSpice macromodel for lithium-ion batteries” S Gold,available at http://www.polystor.com

[0199] 4. “An introduction to cap-XX Pty Ltd and supercpacitors” cap-XXPty Ltd, January 1999

[0200] 5. “General packet radio service in GSM” J Cai & D J Goodman,IEEE Communications Magazine, October 1997, pp122-131

1. An energy storage device including: a battery having a predeterminedinternal resistance R and two terminals for allowing electricalconnection to the battery; and a supercapacitor connected in parallelwith the terminals and having a predetermined equivalent seriesresistance ESR, where ESR<0.5.R.
 2. A device according to claim 1wherein the ESR<0.35.R.
 3. A device according to claim 2 wherein theESR<0.25.R.
 4. A device according to claim 1 wherein the capacitanceprovided by the supercapacitor is sufficient for the pulsed load profileto limit the battery current to a predetermined maximum.
 5. A deviceaccording to claim 1 wherein the supercapacitor provides a substantiallyconstant current as the energy storage device discharges.
 6. A deviceaccording to claim 1 including a housing for containing both the batteryand the supercapacitor, the terminals being accessible from outside thehousing for connecting to a load.
 7. A power supply for a portableelectronic device, the power supply including an energy storage deviceaccording to claim 1 and supply rails for engaging the terminals of theenergy storage device.
 8. A power supply according to claim 7 whereinthe supply rails selectively engage the terminals.
 9. A power supplyaccording to claim 8 wherein the terminals are moved out of engagementwith the supply rails to allow the like terminals of a like energystorage device to be moved into engagement with the supply rails.
 10. Anenergy storage device including: a battery for providing a batterycurrent and having two terminals for electrically connecting with aload; and a supercapacitor connected in parallel with the terminals andhaving a predetermined capacitance that, in use, limits the batterycurrent to a predetermined threshold.
 11. A device according to claim 10wherein the load draws a pulsed current from the energy storage device.12. A power supply including: a battery for providing a battery currentand having two terminals for electrically connecting with a load thatdemands a pulsed current; and a supercapacitor connected in parallelwith the terminals for maintaining the ratio of the RMS value of thebattery current and the average value of the battery current at lessthan about 1.5.
 13. A power supply according to claim 12 wherein thesupercapacitor maintains the ratio of the RMS value of the batterycurrent and the average value of the battery current at less than about1.3.
 14. A power supply according to claim 12 wherein the supercapacitormaintains the ratio of the RMS value of the battery current and theaverage value of the battery current at less than 1.1.
 15. An energystorage device including: a battery for providing a battery current andhaving two terminals for electrically connecting with a load thatdemands a pulsed current; and a supercapacitor connected in parallelwith the terminals for maintaining the ratio of the RMS value of thebattery current and the average value of the battery current at lessthan about 1.5.
 16. An energy storage device according to claim 15wherein the supercapacitor maintains the ratio of the RMS value of thebattery current and the average value of the battery current at lessthan about 1.3.
 17. An energy storage device according to claim 15wherein the supercapacitor maintains the ratio of the RMS value of thebattery current and the average value of the battery current at lessthan 1.1.
 18. A power supply including: a battery having two terminalsfor electrically connecting with a load that demands a pulsed current;and a supercapacitor connected in parallel with the terminals formaintaining the ratio of the range of instantaneous power provided bythe battery and the average value of the power provided by the batteryat less than a predetermined threshold.
 19. A power supply according toclaim 18 wherein the predetermined threshold is 1.5.
 20. A power supplyaccording to claim 18 wherein the predetermined threshold is
 1. 21. Apower supply according to claim 18 wherein the predetermined thresholdis 0.3.
 22. An energy storage device including: a battery having twoterminals for electrically connecting with a load that demands a pulsedcurrent; and a supercapacitor connected in parallel with the terminalsfor maintaining the ratio of the range of instantaneous power providedby the battery and the average value of the power provided by thebattery at less than a predetermined threshold.
 23. An energy storagedevice according to claim 22 wherein the predetermined threshold is 1.5.24. An energy storage device according to claim 22 wherein thepredetermined threshold is
 1. 25. An energy storage device according toclaim 22 wherein the predetermined threshold is 0.3.